source:http://ezinearticles.com/?id=2205422

Do you ever feel indecisive when selecting a lens for your DSLR? I know it is very annoyance, because cost of lens is one of the consideration.

So, before choosing a lens, ask yourself what you need, what is the object you want to captured using the lens? So, below is the three main factor that need to be considered before you buy your lens to suit your DSLR camera.

1.Focal Length
2.Prime or Zoom
3.Maximum Aperture

Focal Length
Distance of the objects is the impact to decide the focal length. Nearer object using shorter focal length, and further object using longer focal length. So, how to decide the number of focal length? Here is some example.

below 35mm: Landscapes and Interiors
35mm to 70mm: Portraits
70mm to 300mm: Portraits and Sports
300mm and higher: Wildlife and Sports

Prime or Zoom
Prime lens is the lens that cannot zoom in or zoom out, but Zoom lens can do so. Zoom actually is controlling the focal length. Probably people will ask, why still have to choose for prime lens if I got better choice that can be zoom as I like? Here is some simple comparison.

Cost: For same specification, prime lens is cheaper than zoom lens.
Quality: Most people are agree this, the picture taken by prime lens is better than zoom lens.
Weight: Prime lens is lighter, zoom lens is heavier.
Speed: In term of aperture, prime lens is faster than zoom lens.

Flexibility: If you want to capture photo for all focal length such as landscape, interior, portrait, sport. You just need one zoom lens to zoom in and zoom out. If you prefer prime lens, may be you need three.
Price: Do you think total cost for three prime lenses will cheaper than one zoom lens?
Portability: Do you think carry three prime lenses will easier than one zoom lens?

Maximum Aperture
Now what is the reason we have to decide the maximum aperture for a lens? Because the lenses have the wider maximum aperture normally are costly. Wider aperture allow more light in, narrower aperture allow less light in. If you taking indoor picture, the light condition indoor is not as good as outdoor, so you need wider aperture to let more light in, if not, the picture you taken will look dark.

Another reason is to suit shutter speed. We need faster shutter speed to take picture for fast object. When your shutter speed is set to very short period, example 1/2000 second (just 0.005 second), and you do not set your aperture wider, then the picture you taken will become underexposure, it look dark.

Last, is about the depth of field, the blurry background is caused by this impact. Wider aperture is decrease the depth of field, background blurry; narrower aperture is increase the depth of field, background clearly.

As conclusion of this topic, it is all about the monetary problem. If I do not consider about my economy status, I will choose focal length with 18mm – 300mm, zoom lens, maximum aperture by 1. But reality is cruel, I have to be more intellect, so I choose focal length 50mm, prime lens, with maximum aperture by 3.5.

DSLR Lens Study

Article Source: http://EzineArticles.com/?expert=Chuan_Wen_Ng

source: http://en.wikipedia.org/wiki/Canon_L_lens

An L lens is a line of SLR photography lenses made by Canon. L lenses are Canon’s top-of-the-line lenses. The “L” officially stands for “Luxury“, a reference to the lenses’ high price and build. Some have rumoured that “L” originally stood for “asphericaL” but this is patently false and has never been substantiated. The use of “ASPH” was common to notate aspherical elements throughout Canon’s and other manufacturers’ histories. Canon produces both L-series zoom and prime lenses for their obsolete FD lens mount and for their current EF lens mount used on all Canon EOS cameras (digital and film).

As of 2007, Canon has not produced any L-series EF-S mount lenses, though the EF-S 17-55mm and EF-S 10-22mm both contain the same high-quality glass elements used in L-series lenses and have comparable image quality to some L-series lenses.Some regard the decision to not designate these lenses as L-series and build the body to L standards a marketing decision.

The lens on the Canon PowerShot Pro1 was designated L-series, and was the first fixed (non-interchangeable) lens so designated.

L-lenses have superior optical performance and are typically built with a solid construction to withstand constant use and harsh conditions. They can be recognized by a red ring around the front part of the lens. Most recent L lenses have sealing to help resist dust and water. L-lenses are typically used by professionals and serious amateurs due to their high price and large mass.

Most L series lenses share a number of common characteristics:

- Tough build, made to withstand the trials on the fields (some incorporating dust and moisture resistant rubber seals).
- At least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass and ground aspherical elements.
- Non-rotating front elements, which are optimal for some filters (e.g. circular polarizers).
- Relatively large apertures compared to other Canon lenses in the same focal lengths.
- Where included, true ring-type USM (ultrasonic motor) and full-time manual focusing.
- Three additional data communication pins on Canon Extender EF compatible lenses, compared to the standard EF mount.

There are some lenses which include one or more of these technologies but which are not designated L-lenses. L-lenses are often equipped with USM and/or IS, but the optical performance is the key criterion.

Larger sized L-lenses, such as the 70-200 mm and 100-400 mm zooms and longer focal length primes (300 mm+), usually have an off-white barrel (sometimes referred to as the color “putty”) to reduce heat absorption under the sun that may otherwise affect the performance of the lens, as well as to identify Canon’s lenses (for example at sporting events). However, shorter focal length L-lenses can be black (such as the Canon EF 24-70 mm f/2.8L and all L-lens primes under 300 mm, with the exception of the discontinued 200 mm f/1.8L and newly announced 200 mm f/2.0L IS.). Therefore L-lenses can be identified by either a lens barrel’s off-white colour or, as on all L-lenses, the distinctive red ring on the lens barrel.

Wide angle L-lenses typically have a gelatin filter holder on the mounting point of the lens, which allows the photographer to cut a small, square piece of gelatin out of a larger filter sheet and place it on the lens. On film cameras, these are typically used to correct the color temperature, but on digital cameras this is largely unnecessary, as the color temperature can be corrected in software. The mount is still commonly used for neutral density gelatin sheets though, especially on certain wide-angle lenses where the protruding front element precludes the use of any screw-in filters. Telephoto L-lenses typically do not have gelatin filter holders, to maintain compatibility with the Canon Extender EFs.

When selecting a dslr lens, what maximum aperture do I need?

For beginner, one important must know before selecting an aperture. You have to know that number of aperture (or aperture value, f) and the size of aperture is inverse. The aperture value normally show as “f/5.6″, or “f-5.6″, or sometimes like “1 : 5.6″.

As smaller aperture number, as wider aperture size.
As larger aperture number, as narrower aperture size.

So, now is the question: What maximum aperture do I need?

1. Depends on the object speed
If an object is moving very fast, I need a very fast shutter speed to take its picture (may be 1/2000 second or 1/4000 second). But, do you realize that, as faster shutter speed, as darker picture. Why? Because faster shutter speed allow less light to in. So, may be I can set the aperture wider to balance this situation, because wider aperture allow more light in.

2. Depends on the lighting condition
If you want to take a picture in a low light environment (such as indoor) without flash, there has two ways to get the light that it needs. First method is adjust your shutter speed (open it for long period, may be take 2 seconds to 5 seconds). Second method is open your aperture as wider as possibble.

3. Depends on the depth of field (DOF)
As some example picture I show on previous post, wider aperture will decrease the depth of field (means make the background become more blurry). So, if you want to focus more on the object you want to capture, and reduce the impact of the busy background, you may need wider aperture.

As the maximum aperture is wider, as the cost of dslr lens more expensive. What lens you choose is still depends on your personal demand. Choose it properly, don’t pay more for the thing that you do not really need.

Below is the sample chart source from http://www.digital-slr-guide.com/

Source: http://www.shortcourses.com/use/using1-9.html

Aperture of lens is exactly like the pupil of eye, it function to control the light amount. The aperture adjusts the size of the opening through which light passes to the image sensor. The aperture can be opened up to let in more light or closed (stopped down) to let in less. In respect to just exposure, smaller apertures let less light strike the image sensor so the image is darker. Larger apertures let in more so it’s lighter.

As the aperture number gets smaller (for example, from f/16 to f/11) the aperture opening gets larger and the image gets lighter. The reason you don’t usually see this effect in your images is because when you or the camera change the aperture, the camera changes the shutter speed to keep the exposure constant.

As with the shutter speed, the aperture also affects the sharpness of your picture, but in a different way. Changing the aperture changes the depth of field, the depth in a scene from foreground to background that will be sharp in a photograph. Smaller apertures increase depth of field while larger ones decrease it. For some pictures—for example, a landscape—you may want a smaller aperture for maximum depth of field so that everything from near foreground to distant background is sharp. But perhaps in a portrait you will want a larger aperture to decrease the depth of field so that your subject is sharp but the background is soft and out of focus.

A small aperture increases depth of field so foreground and background are sharp (top) and a large aperture decreases depth of field so the background is soft (bottom).

Aperture settings are called f-stops and indicate the size of the aperture opening. Each f-stop lets in half as much light as the next larger opening and twice as much light as the next smaller opening. From the largest possible opening to increasingly smaller ones, the f-stops have traditionally been those shown to the left. No lens has the full range of settings; for example, the standard lens on a digital camera will range from about f/2 to about f/16. Notice that as the fstop number gets larger (f/8 to f/11, for example), the aperture size gets smaller. This may be easier to remember if you think of the f-number as a fraction: 1/11 is less than 1/8, just as the size of the f/11 lens opening is smaller that the size of the f/8 opening. Many high-end digital cameras have added one or two stops between each of the traditional ones. In the table to the left one-third and one-half stops are shown in red and blue respectively.

How wide you can open the aperture depends on the len’s maximum aperture— its widest opening. The term “fast lens” usually applies to lenses that can be opened to a wide maximum aperture for the focal length. For example, a lens with a maximum aperture of f/1.8 opens wider, and is faster, than a lens with a maximum aperture of f/2.6. Faster lenses are better when photographing in dim light or photographing fast moving subjects. With most, but not all, zoom lenses the maximum aperture changes as you zoom the lens. It will be larger when zoomed out to a wide angle, and smaller when zoomed in to enlarge a subject.

Tips: To get smaller apertures increase the ISO. To get larger apertures, use a neutral density filter.

For DSLR beginner, we always see the lens with the number such as 16-35mm, 24-70mm, 70-200mm. After that I know that’s call ‘Focal Length’, but as a beginner, i don’t even know what is focal length.

What is Focal Length?

According to the description from wikipedia, the focal length of an optical system is a measure of how strongly it converges (focuses) or diverges (diffuses) light.

The picture above i “borrow” from Understanding Camera Lenses. From this picture, we can know that:
- as the focal length shorter, as the angle of view wider
- as the focal length longer, as the angle of view narrower

Angle of view wider, means that the object can be focus is nearer. So normally those lenses with short focal length (below 35mm) is for wide angle use, focal length with 35mm to 70mm is normal use (example: portrait), and the 70mm and above is for telephoto (example: sports).

For more information about DSLR Lens, may refer Understanding Camera Lenses.